1. Field of the Invention
The present invention relates to a telephone line tester and, more particularly, to a telephone line tester which can be positioned close to customer telephony equipment and communicate test results to a test controller positioned remote from the customer telephony equipment.
2. Background Art
Heretofore, customer telephony equipment was connected to a switch via copper wire pairs. The switch enabled telephony equipment of one customer to be connected to telephony equipment of another customer connected to the same switch or to another switch connected thereto. In order to test the customer telephony equipment, test equipment connected to the switch was connected thereby to a select one of the customer telephony equipment. Selectively connecting the customer telephony equipment thereto enabled the test equipment to test the customer telephony equipment for proper operation.
The inherent resistance of the copper wire pairs utilized to connect customer telephony equipment to the switch limited the effective distance of the connection between each customer telephony equipment and the switch. This limitation required numerous interconnected switches to be distributed throughout a service area to provide telephony service to customer telephony equipment in the service area.
To increase the distance between the switch and each customer telephony equipment, a digital loop carrier system can be positioned between the switch and the customer telephony equipment. The digital loop carrier system enhances the service area of each switch by providing a digital communication network for carrying telephony signals digitally over a significant portion of the path, for example, via a fiber optic cable, between the switch and one or more customer telephony equipment. The digital loop carrier system converts electrical signals transmitted on each copper wire pair into optical signals that can be transmitted over longer distances than the inherent resistance of each copper wire pair would permit. Customer telephony equipment positioned close to the switch can be connected directly thereto.
A problem with the digital loop carrier system is that it is necessary to connect a copper bypass pair in parallel with the fiber optic cable to facilitate testing of the customer telephony equipment. One end of this copper bypass pair is connected to a pair gain test controller which is connected between the test equipment and the switch. The other end of the copper bypass pair is connected to an end of the digital loop carrier system opposite the switch for connection to customer telephony equipment. The pair gain test controller enables the test equipment to be selectively connected to customer telephony equipment connected to the end of the digital loop carrier system opposite the switch via the copper bypass pair or to customer telephony equipment connected directly to the switch via a copper wire pair. Problems with the copper bypass pair running parallel to the fiber optic cable include the susceptibility of the copper bypass pair to corrosion and breaking over time, variances in resistance of the copper bypass pair due to changes in temperature, the need for the test equipment to compensate for the increased distance between the test equipment and the customer telephony equipment and reduced testing accuracy due to electrical impairments occasioned by the copper bypass pair.
It is, therefore, an object of the present invention to provide a low cost and flexible telephone line tester which can be positioned at an end of a digital loop carrier system adjacent customer telephony equipment and which can be utilized to test the customer telephony equipment in a manner similar to test equipment heretofore positioned adjacent the switch side of the digital loop carrier system. It is an object of the present invention to avoid the use of a copper bypass pair in parallel with a fiber optic cable in order to test customer telephony equipment. Still other objects of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.
Accordingly, I have invented a telephony test system for testing customer telephony equipment. The telephony test system includes a test control computer configured to supply an electrical test request signal and to receive an electrical test result signal. A central office terminal is connected between the test control computer and a fiber optic cable. The central office terminal is configured to receive the electrical test request signal from the test control computer, to convert the electrical test request signal to a corresponding optical test request signal and to supply the optical test request signal to the fiber optic cable. The central office terminal also receives an optical test result signal from the fiber optic cable, converts the optical test result signal to the electrical test result signal and supplies the electrical test result signal to the test control computer. A remote terminal is connected between an end of the fiber optic cable opposite the central office terminal and telephony equipment of a plurality of customers. The remote terminal is configured to receive the optical test request signal from the fiber optic cable and to convert the optical test request signal to the electrical test request signal. The remote terminal also receives the electrical test result signal, converts the electrical test result signal to the optical test result signal and supplies the optical test result signal to the fiber optic cable. A line test unit (LTU) has a controller between the remote terminal and a high voltage amplifier configured to be connected by the remote terminal to select customer telephony equipment to supply a test signal thereto. The LTU includes a power supply configured to be controlled by the controller to supply electrical power to the high voltage amplifier. The controller causes the high voltage amplifier to supply a test signal to the customer telephony equipment. The controller determines electrical power dissipated by the high voltage amplifier supplying the test signal to the customer telephony equipment and controls the power supply to adjust the voltage supplied to the high voltage amplifier to avoid electrical power dissipated by the high voltage amplifier from exceeding a desired maximum electrical power dissipation.
The power supply can supply to the high voltage amplifier a differential voltage having a maximum value of xc2x1190 volts. The controller can include a digital signal processor (DSP) operating under control of a software program and a logic circuit controlled by the DSP, with the logic circuit or the DSP implementing a communication interface which receives the electrical test request signal from the remote terminal and which supplies the electrical test result signal to the remote terminal.
The LTU can include a digital-to-analog converter (DAC) to receive digital signals from the controller and to produce an analog signal as a function of the received digital signals. A successive approximation network can be connected to receive the analog signal from the DAC, to compare the analog signal received from the DAC with a measured electrical condition of the customer telephony equipment and to provide to the controller a binary signal indicative of the comparison. A receive channel filter can filter the measured electrical condition and supply the filtered and measured electrical condition to the successive approximation network for comparison. A sample-and-hold switch network can receive the measured electrical condition and supply the measured electrical condition to the successive approximation network for comparison. The controller connects the successive approximation network to selectively receive the filtered and measured electrical condition from the receive channel filter and the measured electrical condition from the sample-and-hold switch network.
The LTU can include a transmit channel filter which receives and filters the analog signal from the DAC and supplies the filtered analog signal to the high voltage amplifier. A transmit/receive (T/R) switch network can selectively connect (i) the transmit channel filter to receive the analog signal from the DAC or (ii) the successive approximation network to receive the filtered and measured electrical condition from the received channel filter. A voiceband transceiver can be connected to receive a digital signal from the controller, to supply to the high voltage amplifier a voiceband signal corresponding to the received digital signal, to receive a voiceband signal from the customer telephony equipment and to convert the received voiceband signal into a digital signal for processing by the controller. An input/output (I/O) switch network can connect the high voltage amplifier to selectively receive (i) the voiceband signal from the voiceband transceiver and the analog signal from the DAC or (ii) the analog signal from the DAC.
The LTU can include a tip terminal and a ring terminal configured to be connected by the remote terminal to a tip circuit and a ring circuit of the customer telephony equipment. A tip I/O signal path and a ring I/O signal path can be connected between the sample-and-hold switch network and the tip terminal and the ring terminal to convey the measured electrical condition of the select customer telephony equipment therefrom to the sample-and-hold switch network. A tip-out (TO) signal path and a ring-out (RO) signal path can be connected to selectively receive the analog signal from the DAC. The TO signal path and the RO signal path include the transmit channel filter. A tip high voltage amplifier can be connected between the TO signal path and the tip terminal and a ring high voltage amplifier can be connected between the RO signal path and the ring terminal. The tip high voltage amplifier and the ring high voltage amplifier comprise the high voltage amplifier. A tip-in (TI) signal path can be connected between the tip terminal and the successive approximation network and a ring-in (RI) signal path can be connected between the ring terminal and the successive approximation network. The TI signal path and the RI signal path include the receive channel filter. A voiceband tip path and a voiceband ring path can be connected between the voiceband transceiver and the TI signal path and the RI signal path, respectively. A tip I/O switch network can be connected between the TO signal path, the voiceband tip path and the tip high voltage amplifier and a ring I/O switch network can be connected between the RO signal path, the voiceband ring path and the ring high voltage amplifier. The tip I/O switch network and the ring I/O switch network comprise the I/O switch network. The tip I/O switch network selectively connects the tip high voltage amplifier to (i) the combination voiceband tip path and TO signal path or (ii) the TO signal path. The ring I/O switch network selectively connects the ring high voltage amplifier to (i) the voiceband ring path and the RO signal path or (ii) the RO signal path.
The controller can control the sample-and-hold switch network and the T/R switch network to selectively connect the successive approximation network to the TO signal path, the RO signal path, the TI signal path, the RI signal path, the tip I/O signal path and the ring I/O signal path.
I have also invented a telephony line test unit having a communication interface connected to communicate with a remote terminal which is connected to communicate with a central office terminal via a digital communication network. The line test unit includes an input/output which is selectively connectable by the remote terminal to customer telephony equipment. A controller receives an electrical test request signal from the remote terminal and a digital-to-analog converter (DAC) controlled by the controller produces an analog signal. A comparator has a first input connected to receive the analog signal from the DAC, a second input connected to receive an analog signal from the input/output of the line test unit and an output which supplies a binary signal to the controller which corresponds to the comparison of the analog signals received at the first and second inputs. A high voltage amplifier selectively receives the analog signal from the DAC and supplies an electrical test signal to the input/output of the line test unit as a function of the analog signal received thereby. An adjustable power supply controlled by the controller supplies to the high voltage amplifier electrical power at a desired potential. In response to receiving the electrical test request signal, the controller causes the high voltage amplifier to supply the electrical test signal to the customer telephony equipment. The controller, the DAC and the comparator coact to determine the response of the customer telephony equipment to the electrical test signal. The controller determines as a function of the supplied test signal and the response of the customer telephony equipment thereto electrical power dissipated by the high voltage amplifier and controls the power supply to adjust the potential of the electrical power supplied to the high voltage amplifier to avoid electrical power dissipated by the high voltage amplifier from exceeding a desired maximum electrical power dissipation.
The line test unit can include a receive channel filter to receive the electrical test signal from the input/output of the line test unit, to filter the received electrical test signal and to supply the filtered electrical test signal to the second input of the comparator. A switch network can connect the second input of the comparator to selectively receive the electrical test signal from the input/output of the test system or the filtered electrical test signal from the receive channel filter. A transmit channel filter can be connected to receive the analog signal from the DAC, to filter the received analog signal and to supply the filtered analog signal to the high voltage amplifier. A voiceband transceiver can be connected to supply a voiceband signal to the high voltage amplifier and to receive a voiceband signal from the input/output of the line test unit. The switch network can connect the high voltage amplifier to selectively receive (i) the voiceband signal from the voiceband transceiver and the analog signal from the DAC or (ii) the analog signal from the DAC.
I have also invented a method of testing customer telephony equipment connected to a switching network with a test system disposed at the switching network. The method includes receiving a test request signal at the test system and the switching network. In response to the switching network receiving the test request signal, an input/output of the test system is connected to the customer telephony equipment. In response to the test system receiving the test request signal and the switching network connecting the input/output of the test system to the customer telephony equipment, a high voltage amplifier of the test system is caused to supply a test voltage to the customer telephony equipment via the input/output of the test system. The electrical power dissipated by the high voltage amplifier is determined during supply of the test voltage thereby. A power supply is controlled to adjust a voltage supplied to the high voltage amplifier to avoid electrical power dissipated during supply of the test voltage thereby from exceeding a desired maximum electrical power dissipation.
The method can also include the steps of measuring with the test system via the input/output thereof a response of the customer telephony equipment to the test voltage and transmitting from the test system a test result signal related to the measured response of the customer telephony equipment.
Lastly, I have invented a test system disposed at a switching network for testing telephony equipment of a plurality of customers connected to the switching network. The test system includes receiver means for receiving a test request signal via the switching network. Measurement means measures electrical conditions of the telephony equipment of one of the plurality of customers and high voltage amplifier means supplies a test voltage to the telephony equipment of the one customer. Control means controls the high voltage amplifier means to supply the test voltage to the telephony equipment of the one customer and controls the measurement means to measure an electrical condition of the telephony equipment of the one customer in response to the test voltage. Power supply means controlled by the control means supplies electrical power to the high voltage amplifier means. Transmitting means transmits a test result signal related to the measured electrical condition of the telephony equipment of the one customer. The control means determines electrical power dissipated by the high voltage amplifier means supplying the test voltage to the telephony equipment of the one customer and controls the power supply means to adjust the voltage supplied to the high voltage amplifier to avoid electrical power dissipated thereby from exceeding a desired maximum electrical power dissipation.